Amplifiers – Hum or noise or distortion bucking introduced into signal...
Patent
1990-06-27
1991-12-24
Mottola, Steven
Amplifiers
Hum or noise or distortion bucking introduced into signal...
330107, H03F 136
Patent
active
050756354
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a device for correcting the phase induced by the class C operation of a solid state amplifier. It is applied in the field of the manufacture of pulse radar transmitters.
2. Background Discussion
In modern radars, the transmitted electromagnetic waves are generated by a device based on semiconductor components using microwave frequency transistors. The characteristics of the radar are directly related to the transfer function. Now, the latter depends on the operating conditions of the system.
In most radar applications, the Doppler effect affects the signals returned by moving targets, allowing the elimination of fixed echoes. Thus, in the case of a pulse compression radar, a frequency shift due to the Doppler effect is added to the phase or frequency encoding.
Now, the quality of the pulse compression radar essentially depends upon the ability to provide a receiving system whose transfer function is strictly the reverse of that of the transmission system. When working with solid state power stages, the amplification stages work in Class C. The peak powers are lower than in the case technologies based on valves (klystrons, Standing Wave Tubes, etc.) but the medium power developed can be high in order to allow a suitable form factor.
The desired powers are obtained by grouping power stages, controlled by low level transistors, in cascade. The final power is obtained by adders (Wilkinson circuits, 3 dB rings, . . . ). These circuits always allow a sufficient power to be maintained even in the case of the failure of several stages which are automatically replaced.
However, power semiconductors are subject to two types of negative phenomena when used in pulse radars. Firstly, the instantaneous power varies during the pulse. Then, the phase varies.
During the progress of the invention, it was discovered that these phenomena were due to considerable variations in the junction temperature of the power transistors in the final stages. In pulse class C, the junctions change from zero dissipation before the rise of the pulse to maximum dissipation when the pulse power is at its maximum value. Now, the efficiency of transistors in this range being of the order of forty per cent, the heat dissipation is high during the duration of the pulse. The junction/casing thermal resistance of each transistor, however low it may be, results in the temperature varying during the pulse instead of remaining constant according to perfect radar theory.
As, in addition, the radars can work in frequency excursion mode or in frequency diversity mode or in a random wobbulated frequency mode to avoid countermeasures, the temperature variations become inhibitory.
In fact, they are responsible for variations in the phase and amplitude of the transmitted signal. In Doppler processing, the problem is further increased by the fact that the radar creates a band of parasitic Doppler frequencies.
The obvious solution which consists in cooling the junctions of the transistors during the relaxation between two pulses cannot be applied here since the widths of the pulses and the relaxation durations can vary considerably with no direct relationship between them.
SUMMARY OF THE INVENTION
It is an object of the present invention to allow an effective control of the phase of the output signal of the power stages of a solid state amplifier operating in class C, even when the the repetition rates are not constant nor even continuously variable.
Another object of the present invention is to propose a simple means of allowing a correction of the transfer function of the radar system which considerably reduces the phase variations in the transmitted pulse whatever the parameters of the system may be: frequency agility or wobbulation in particular. In fact, the present invention relates to a device for correcting the phase induced by the class C operation of a solid state amplifier of pulse signals. The invention is characterized in particular by the fact that the ampli
REFERENCES:
patent: 3346822 (1967-10-01), Levy et al.
patent: 4122399 (1978-10-01), Heiter et al.
patent: 4276514 (1981-06-01), Huang
patent: 4554514 (1985-11-01), Whartenby et al.
patent: 4600892 (1986-07-01), Wagner et al.
Electronics Letters, vol. 7, No. 7, 8 Apr. 1971, Hitchin GB pp. 145-146, T. Arthanayake et al.: "Linear Amplification Using Envelope Feedback", p. 145.
Boulanger Alain
Creff Jacques
"Thomson-CSF"
Mottola Steven
LandOfFree
Device for correcting the phase induced by the class C operation does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Device for correcting the phase induced by the class C operation, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Device for correcting the phase induced by the class C operation will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-45852